Projector for analytical viewing of moving pictures

ABSTRACT

The moving action is stopped and started by a solenoid, with diverse methods of control to stop the action or to show the successive frames on the film at varying rates such as 1 per second to 8 per second. To interrupt the advancing of the film through the light beam, the conventional claw-actuating cam is retracted so that it does not thrust the claw into engagement with the film apertures. At the same time, the auxiliary feed of the film toward and from the loop advanced by the claw is interrupted by axially shifting a clutch-brake member. A single solenoid-actuated plunger acts on both the clutch-brake member and the claw-actuating cam. The shutter operates continuously, maintaining constant light intensity. A timing cam rotates continually with the shutter to time the actuation of the solenoid accurately for resuming all feeding operations. Another cam, rotating with the drive for the auxiliary feeds controls the timing for the deenergization of the solenoid to discontinue the feed operations. The solenoid-actuated plunger acts directly on the switch-brake member, and acts on the claw-actuating cam by a pin extending through the drive shaft into which the plunger projects, the projecting ends of the pin riding on a hub on the claw-actuating cam. This hub rotates with respect to the pin during times of interrupted feed. An air jet blows on the film and non the optical member adjacent to it on the lamp side of the film, providing thoroughly adequate cooling of the film even when stopped indefinitely. Other details ensure reliable operation.

United States Patent SENSITIVITY CONTROL DEVICE IN RECEIVERS FOR OPTICALSIGNALS 2 Claims, 1 Drawing Fig.

l References Cited UNITED STATES PATENTS 3.5|6,75l 6/!970 Fruengel H356/4 Primary Examiner- Rodney D. Bennett, Jr. Assistant Examiner-J. M.Potenza Altomeys- Hane and Baxley ABSTRACT: A photomultiplier forgenerating electric pulses in response to impinging light has connectedto its output a signal transmission device including threshold means sothat pulses generated by the photomultiplier are passed through thetransmission device only if their amplitude exceeds a threshold value. Apulse frequency detector is connected to the output ofthe transmissiondevice to produce an output signal depending on the pulse repetitionfrequency U.S. (,l 35 45 of the pulses passed by the transmissiondevice. This output Int. Cl 11 3 03 signal is applied to control therelation between the threshold Field otSeareh 355/4 value and theamplitude ofthe pulses generated by the photo- 5;250/207.7l.5multiplier.

PHOTO -MULT|PLIE.R AMPLIFIER 7 PULSE. FREQUENCY D CT'O CONTROLLED ET: RVOLTAGE SOURCE 4 REFERENCE SIGNAL COM PARATOK PATENTEU AUG 7 19?: 3 600O7 2 mm 1 OF INVENTORS BY RIC/MRO L SH/Rl E V .QOJO, @MMW Arr'rsPATENTED AUG! 7 Ian SHEU 2 BF 2 IN VEN'TORS MA Y WA 5 TL BY RICHARD LSH/Rl E Y Davao, lemma M Arrrs SENSITIVITY ('ONTROL DEVICE IN RECEIVERSFOR OPTICAL SIGNALS BACKGROUND OF THE INVENTION The invention relates toa device for sensitivity control in receivers for the reception ofoptical signals in the form of short pulses and particularly receiversfor range finders operating with light pulses generated by a laser andcomprising a photomultiplier tube which is arranged to receive theoptical signals and to convert these signals into electric pulses and toamplify these pulses. and a signal transmission device. which isconnected to the output of the photomultiplier and comprises a thresholddevice which permits transmission only of those signals whose amplitudeexceeds a threshold value.

The current generated by a photomultiplier in response to impinginglight of low intensity is not a continuous current but consists ofdiscrete pulses of varying amplitude. This is also the case when thephotomultiplier is subjected to a steady illumination of low intensity.

The optical system in a receiver for range finders operating with lightpulses generated by a laser is so designed that the photomultiplier asfar as possible is only actuated by the light pulses transmitted by thelaser and reflected from some object. Therefore, the optical system hasa very small field of view and it usually comprises a filter, e.g., aninterference filter, which transmits only light having the wave lengthof the laser light. However, in spite of these precautions it isimpossible to entirely prevent other light than the laser light fromentering the optical system and impinging upon the photomultiplier.Also, the photomultiplier generates a certain "darkness current" evenwhen it is not illuminated. Thus, in addition to the pulses generated bythe laser light, in the following named echo pulses. pulses caused bylight from the environment and the background and pulses correspondingto the darkness current of the photomultiplier are appearing at theoutput of the photomultiplier. These nondesirable pulses, in thefollowing named noise pulses, are applied along with the echo pulses tothe signal transmission device. Thus. there arises the problem ofseparating the echo pulses from the noise pulses and preventing thelatter pulses from being forwarded by the signal transmission device tothe counting means of the range finder.

The noise pulses have amplitudes varying at random, but the number ofnoise pulses appearing per unit of time whose amplitude exceeds acertain level is less the higher this level is. The signal transmissiondevice connected to the photomultiplier can be provided with means, inthe following named threshold means, which operate in such manner thatonly input signals having an amplitude exceeding a certain level, thethreshold level, are transmitted. By making the threshold levelsufficiently high it is possible to prevent a large portion of the noisepulses. i.e.. those noise pulses whose amplitude exceeds the thresholdlevel, from'passing through the signal transmission device. Some noisepulses can be permitted to pass throught the signal transmission device,provided that the number of such pulses per time unit is small so thatthe probability of such a noise pulse appearing during the briefinterval between the transmission and the reception of a laser pulse issmall, for instance 1%. This can readily be achieved by making thethreshold level sufi'tciently high.

However, the number of noise pulses appearing per time unit and having alarge amplitude will vary considerably with the illumination conditionsin the environment and the background of the range finder and theobject. to which the distance is to be measured. 1f the threshold levelis so chosen that the number of transmitted noise pulses becomessufi'tciently small even under very unfavourable illuminationconditions, this leads to the result that the range finder will have asmall maximum range. The amplitude of the echo pulse must of courseexceed the threshold level in order that is shall he passed through thesignal transmission device. and since the amplitude of the echo pulse isless the longer the distance it has travelled. echo pulses from objectssituated at large distances will not have a sufficiently large amplitudeupon reception to exceed the threshold. Thus. the threshold leveldetermines the maximum range of the range finder. A threshold levelwhich has been chosen with regard to the worst possible illuminationconditions is unnecessarily high at better illumination conditions,i.e.. such illumination conditions which cause a smaller number of noisepulses having a large amplitude. As a consequence the maximum range ofthe range finder under better illumination conditions will beunnecessarily limited, since the threshold value could then be lower sothat even weaker echo pulses could pass through the signal transmissiondevice.

It is an object of the present invention to eliminate this drawback andto provide a sensitivity control so that the threshold level isautomatically adapted to the illumination conditions.

SUMMARY OF THE INVENTION In accordance with the invention a receivingsystem of the kind described above comprises pulse frequency detectingmeans for producing an output signal depending on the pulse repetitionfrequency of the pulses passed by the signal transmission means, andmeans for applying said output signal to control the relation betweensaid threshold value and the amplitude of the puses emanating from thephotomultiplier.

In a preferred embodiment of the invention the output signal from thepulse frequency detecting means is applied to a comparison device whichalso receives a reference signal from a signal source producing areference signal corresponding to a predetennined pulse repetitionfrequency. The comparison device produces an output signal representingthe difference between the output signal from the pulse frequencydetecting means and the reference signal. This difference signal is usedto control the relation between the threshold value and the amplitude ofthe pulses emanating frown r e ni a i u If, as is usually the case, thesignal transtnission device connected to the output of thephotomultiplier includes an amplifier, the threshold means is preferablyincluded in the amplifier. In such case the pulse frequency detector ispreferably connected to the output of the amplifier, and the controlmeans are arranged to control the threshold value under the control ofthe output signal from the pulse frequency detector or the comparisondevice.

However, in some cases the amplification effected by the photomultipliermay be so large that an amplifier can be dispensed with in the signaltransmission device. In such case it may be preferable to let thethreshold means have a constant threshold value and to control therelation between the threshold value and the amplitude of the pulsesemanating from the photomultiplier by making the output signal of thepulse frequency detector or the comparison device actuate the controlmeans for controlling a feed voltage for the photomultiplier therebycontrolling the amplitude of the outgoing pulses.

TI: reference signal from the reference signal source is controlled sothat it corresponds to a pulse repetition frequency which makes theprobability of a noise pulse appeariw the time interval between thetransmission and reception of the laser pulse sufficiently small. Theoutput signal from the pulse frequency detector or the comparison deviceacts upon the control means for the threshold value in such manner thatif the pulse repetition frequency as detected by the pulse frequencydetector becomes too large, the threshold value is increased and viceversa.

DETAILED DESCRIPTION In the following the invention will be describedmore in particular with reference to the accompanying drawing whichshows a block diagram of a device in accordance with the invention.

In the drawing 1 designates a photomultiplier tube which is included inknown manner in the optical system of the receiver so that its photocathode is hitby the light entering through the optical system. Thislight is indicated in the drawing by arrows at the lefthand side of thephotomultiplier l. The output of the photomultiplier is connected to anamplifier 2 which is so designed that only input signals having anamplitude exceeding a certain threshold value are amplified and passedto the output of the amplifier. The signals appearing at the output ofamplifier 2 are transmitted over a line 3 to utilization means (notshown). e.g.. to means for measuring the time interval between thetransmission and the reception of a laser pulse.

To the output of amplifier 2 is also connected a pulse frequencydetector 4 of known kind which produces an output signal. e.g.. a directvoltage. whose intensity varies with the pulse repetition frequency. Theoutput signal from the pulse frequency detector is applied to acomparison device 5. This comparison device also receives a referencesignal. e.g., a direct voltage. from a reference signal source 6. Thecomparison device 5 generates an output signal depending on thedifference between the signals supplied from the devices 4 and 6. Thisoutput signal is transmitted over line 7 to the control means forcontrolling the threshold value of the amplifier.

The various parts represented by blocks in the drawing may each bedesigned in known manner. and therefore they will not be described indetail. The control means for controlling the threshold value of theamplifier may for instance consist of a rectifier which is given acertain bias which must be exceeded by the signal voltage in order thatan output voltage shall be produced. Preferably the rectifier has afixed bias on which the output voltage from the comparison device 5 issuperposed. The reference signal source 6 is preferably so designed thatthe reference signal can easily be adjusted to any desired value.

Alternatively the output of the comparison device 5 may be connected tocontrol means for controlling the feed voltages of the electrodes of thephotomultiplier. Such a connection is indicated in the drawing by thedotted line 8. The voltage feed equipment and the associated controlmeans can be designed in known manner, and therefore they have beenindicated only in the form of a block 9 in the drawing.

lclaim:

l. A device for sensitivity control in receivers for receiving opticalsignals in the form of short pulses. particularly receivers for rangefinder systems operating with light pulses generated by a laser. saidreceiver comprising a photomultiplier for receiving the optical signals.converting these signals into electric pulses and amplifying thesepulses, and signal transmission means connected to the output of saidphotomultiplier. said signal transmission means comprising thresholdmeans permitting the transmission only of signals whose amplitudeexceeds a threshold value, characterized by pulse frequency detectingmeans for producing an output signal depending on the pulse repetitionfrequency of the pulses passed by said signal transmission means. andmeans for applying the output signal from said pulse frequency detectingmeans to control a supply voltage for said photomultiplier therebycontrolling the amplitude of the pulses generated by saidphotomultiplier and accordingly the relation between said thresholdvalue and the amplitude of the ls ssmsnatmsfrsmsj hstp lu tk- 2. Adevice for sensitivity control in receivers for receiving opticalsignals in the form of short pulses, particularly receivers for rangefinder systems operating with light pulses generated by a laser, saidreceiver comprising a photomultiplier for receiving the optical signals,converting these signals into electric pulses and amplifying thesepulses, and signal transmission means connected to the output of saidphotomultiplier, said signal transmission means comprising an amplifierincluding threshold means permitting the transmission only of signalswhose amplitude exceeds a threshold value, characterized by pulsefrequency detecting means connected to the output of said amplifier forproducing an output signal depending on the pulse repetition frequencyof the pulses passed by said signal transmission means, and controlmeans responsive to the output signal from said pulse frequencydetecting means for applying said output signal to said threshold meansto control the relation between said threshold value and the amplitudeof the pulses emanating from the photomultiplier.

1. A stop motion projector for analytical viewing including a constantlydriven shutter; a cLaw-actuating means including a cam constantlyrotating with the shutter; auxiliary drive means for auxiliary film feedmeans, normally rotating with the shutter; and means for interruptingthe film feed comprising a power-actuated plunger, a friction clutchmember actuated by the plunger to couple the shutter and auxiliary drivemeans for joint rotation upon actuation of the plunger in the startingdirection; and disabling means actuated by the same plunger forrendering the claw-actuating means ineffective to advance the film, saidfriction clutch and disabling means being both operated by oppositemovement of the plunger for simultaneous engagement of the clutch andrestoration of the effectiveness of the clawactuating means.
 2. A stopmotion projector for analytical viewing including a constantly drivenshutter; a claw-actuating cam constantly rotating with the shutter butaxially movable; auxiliary drive means for auxiliary film feed means,normally rotating with the shutter; and means for interrupting the filmfeed comprising a solenoid, a plunger actuated by the solenoid along theaxis of the shutter, a clutch member axially actuated by the plunger tofrictionally couple the shutter and auxiliary drive means for jointrotation upon actuation of the plunger in the starting direction; ashaft extending through the shutter and claw-actuating cam along theaxis thereof to drive the auxiliary drive means; and a pin extendinglaterally from said shaft and movable axially by the plunger for movingthe claw-actuating cam axially in one direction, said cam and its clawbeing biased in the opposite axial direction, whereby movement of theplunger simultaneously shifts the claw-actuating cam to its effectiveposition and engages the clutch for drive of the auxiliary feed means.3. A stop motion projector for analytical viewing including a constantlydriven shutter; a claw-actuating means including a cam constantlyrotating with the shutter; auxiliary drive means for auxiliary film feedmeans, normally rotating with the shutter; and means for interruptingthe film feed comprising a power-actuated plunger, a frictionclutch-brake member actuated by the plunger to couple the shutter andauxiliary drive means for joint rotation upon actuation of the plungerin the starting direction and for stopping the auxiliary drive meansupon actuation of the plunger in the opposite direction; and disablingmeans actuated by the same plunger for rendering the claw-actuatingmeans ineffective to advance the film, said friction clutch-brake memberand disabling means being both operated by starting direction movementof the plunger for simultaneous engagement of the clutch and restorationof the effectiveness of the claw-actuating means.
 4. A stop motionprojector for analytical viewing including a constantly driven shutter;claw-actuating means including a cam constantly rotating with theshutter but axially moveable; auxiliary drive means for auxiliary filmfeed means normally rotating with shutter; and means for interruptingthe film feed comprising a power-actuated plunger, a friction clutchmember axially actuated by the plunger to frictionally couple theshutter and auxiliary drive means for joint rotation upon actuation ofthe plunger in the starting direction; a shaft extending through theshutter and claw-actuating cam along the axis thereof to drive theauxiliary drive means; and a pin extending laterally from said shaft andmovable axially by the plunger for moving the claw-actuating cam axiallyin one direction, said claw-actuating means being biased in the oppositeaxial direction; whereby movement of the plunger in the startingdirection shifts the pin and claw-actuating cam to its effectiveposition and simultaneously engages the clutch for drive of theauxiliary feed means.
 5. A stop motion projector for analytical viewingincluding a constantly driven shutter; a claw-actuating means includinga cam constantly rotating with the shutter; auxiliary drive meaNs forauxiliary film feed means, normally rotating with the shutter; and meansfor interrupting the film feed comprising a power-actuated plunger, afriction clutch member actuated by the plunger to couple the shutter andauxiliary drive means for joint rotation upon actuation of the plungerin the starting direction; and disabling means actuated by the sameplunger for rendering the claw-actuating means ineffective to advancethe film, said friction clutch and disabling means being both operatedby opposite movement of the plunger for simultaneous engagement of theclutch and restoration of the effectiveness of the claw-actuating means;and cam means, rotatable with the claw-actuating cam for timing theplunger movements relative to the cycle thereof.
 6. A stop motionprojector for analytical viewing including a constantly driven shutter;a claw-actuating means including a cam constantly rotating with theshutter but axially movable; auxiliary drive means for auxiliary filmfeed means, normally rotating with the shutter; and means forinterrupting the film feed comprising a solenoid-actuated plungershiftable along the axis of the shutter, a clutch-brake member securedto the plunger to engage the shutter to be rotated with it, uponactuation of the plunger in the starting direction; an axially fixedshaft having telescopic and keyed engagement with the plunger to bedriven by the clutch member and extending through the shutter andclaw-actuating cam along the axis thereof to drive the auxiliary drivemeans; and a transversely disposed pin extending laterally from saidshaft through slots and movable axially of the shaft in said slots,moved axially by the plunger and moving the claw-actuating cam axiallyin one direction, said claw-actuating means being spring actuated in theopposite axial direction; said cam and pin being free for relativerotation between them.